The invention relates generally to heat-exchange arrangements.
Heat-exchangers are known which include a housing and a nest or bundle of tubes arranged interiorly of the same. A cooling medium flows through the tubes whereas a fluid to be cooled flows through the housing and impinges the tubes exteriorly thereof. Baffles are arranged inside the housing for changing the direction of flow of the fluid to be cooled. By virtue of the impingement of the fluid to be cooled upon the outside surfaces of the conduits or tubes, the cooling medium flowing in the conduits may undergo vaporization.
Heat-exchangers of this type are utilized in cooling circuits which include a vaporizer, a compressor, a condenser and a pressure-reducing valve. Here, the cooling medium flows along a closed path. The cooling medium enters the heat-exchanger in liquid form and is vaporized therein by virtue of the heat-exchange which it undergoes with a fluid to be cooled, that is, the heat-exchanger serves as a vaporizer. After leaving the heat-exchanger, the cooling medium is compressed, condensed and subjected to a pressure reduction. In this manner, the cooling medium is returned to its original liquid state. The liquid cooling medium is then re-admitted into the heat-exchanger.
The introduction of the cooling medium into a heat-exchanger of the type described above is generally controlled by means of a thermostatic expansion valve located upstream of the inlet for the liquid cooling medium and the opening and closing of which are effected by means of external pressure equalization. The open and closed phases of the expansion valve are regulated in dependence upon the output from a pressostat and a thermostat arranged downstream of the outlet opening for the vaporized cooling medium. This regulation resides in that liquid cooling medium is permitted to enter the heat-exchanger only when the pressostat and the thermostat register a completely gaseous condition for the cooling medium at the outlet of the heat-exchanger. This design serves not only as a means for controlling the operation of the heat-exchanger but serves also as a safety measure for the compressor arranged downstream of the outlet opening for the cooling medium. Thus, impingement of the compressor by drops of liquid cooling medium sucked in by the compressor may cause severe damage to the latter.
The efficiency of a heat-exchanger of the above type with respect to the cooling circuit has been found to be no better than that of the tube which exhibits the poorest heat transfer and which, concomitantly, provides for the poorest vaporization of cooling medium within the nest of tubes. The reason is that the cooling medium flowing in the tube having the poorest heat transfer characteristics passes through the tube in liquid form and causes the thermostat and pressostat to close the expansion valve located in the region of the inlet of the heat-exchanger. The result is that the remaining tubes of the nest, which provide for better vaporization, contain less cooling medium than they are capable of vaporizing on the basis of their design. In practice, the gaseous phase of the cooling medium is then disadvantageously shifted towards the inlet of the heat-exchanger, that is, complete vaporization of the cooling medium occurs closer to the inlet of the heat-exchanger than would be the case otherwise. As a consequence, the efficiency of the heat-exchanger and, concomitantly, the efficiency of the entire cooling circuit, is substantially decreased.
In order to alleviate these disadvantages to some extent, it has been necessary in the past to either construct larger heat-exchangers or to arrange a number of smaller heat-exchangers in series. However, this not only results in large space requirements and high costs but also requires the performance of more work at the suction side of the compressor.
A heat-exchanger of the type under consideration which has become known from the DT-AS 1,077,681 attempted to overcome the foregoing disadvantages by conveying the cooling medium through the nest of tubes progresively along a plurality of paths. Here, covers are provided at the opposite ends of the nest of conduits, the cover serving as baffles which cause the cooling medium exiting from one of the conduits to flow into another of the conduits. The covers are provided with separating webs and connecting members on their inner sides. On the one hand, the separating webs and connecting members are arranged so that the cooling medium is initially introduced into the conduits constituting the uppermost horizontal row of the nest and into the conduits constituting the lowermost horizontal row of the nest. On the other hand, the separating webs and connecting members are arranged so that the cooling medium is each time deflected only from one horizontal row of conduits to the immediately adjacent overlying or underlying row of conduits. The separating webs and connecting members are further arranged in such a manner that the cooling medium exits from the heat-exchanger via one of the covers and at a level of the latter corresponding approximately to the horizontal symmetry axis thereof. Moreover, provision is made for a progressive increase in the volume interiorly of the conduits so as to adjust for the increase in volume of the cooling medium as it vaporizes. The preceding measures are intended to achieve a better vaporizing effect and an accompanying improved efficiency. Nevertheless, even with this heat-exchanger it is not possible to avoid the passsage of cooling medium through the nest in liquid phase. One of the reasons for this resides in that the housing in which the nest of tubes is accommodated has an internal cross-section which is of circular configuration. Thus, on the one hand, despite the provision of baffles, the fluid to be cooled impinges the external surfaces of the tubes with varying flow velocities due to the circular configuration of the housing. On the other hand, so-called "dead edges" exist in the housing and the tubes arranged in these dead edges can be only partially impinged by the fluid to be cooled. Particularly dangerous conditions exist here in view of the danger that the cooling medium will pass through the nest of tubes in liquid phase.
It may be seen, therefore, that improvements in the state of the art are desirable.